The invention is related to the field of microelectromechanical systems, and, in particular, to a particle filter for a partially enclosed microelectromechanical system that reduces or prevents particulate contamination of the micro-devices that make up the system.
There are a number of fabrication technologies, collectively known as micromachining, for producing microelectromechanical systems. One type of micromachining process is surface micromachining. Surface micromachining involves deposition and photolithographic patterning of alternate layers of structural material (typically polycrystalline silicone, termed polysilicon) and sacrificial layers (typically silicon dioxide, termed oxide) on a silicon wafer substrate material. Using a series of deposition and patterning, functional devices are constructed layer by layer. After a device is completed, it is released by removing all or some of the remaining sacrificial material by exposure to a selective etchant such as hydrofluoric acid, which does not substantially attack the polysilicon layers.
Unfortunately, it is a problem in the art of microelectromechanical systems to prevent particle contamination. Particle contamination can potentially ruin an entire system by interfering with the electrical signals and/or mechanical movements of some or all of the electrical and/or mechanical devices.
One solution to this problem is to provide a cover over the microelectromechanical system that at least partially encloses the system and protects enclosed components from particle contamination. When covers are utilized or otherwise when there are structural features having substantial coverage area, etch release apertures in such structure are typically utilized to introduce etchant for removal of the sacrificial material and release of internal devices. These etch release apertures typically include openings on the order of about 1.25 microns in size. Unfortunately, however, these openings still permit the introduction of particles that are large enough to cause mechanical obstructions or electrical shorts in the internal devices.
It is therefore an object of the present invention to provide a particle filter and method of fabricating the same for microelectromechanical systems that are at least partially enclosed by a cover or other similar structure. It is another object of the present invention to provide a plurality of configurations for the particle filter to accommodate different spatial limitations within microelectromechanical systems. It is still yet another object of the present invention to provide a particle filter that may be formed around etch release apertures in a cover to trap particles introduced through such apertures within the filter, thereby preventing contamination of internal components.
In carrying out the above objects, and other objects, features, and advantages of the present invention, a particle filter is provided that includes a first structural layer forming a filter bottom and a second structural layer forming a filter wall. The filter bottom and filter wall are interconnected by at least one support feature to define a particle trap between the filter wall and filter bottom. In that regard, the particle trap may be a gap formed by mating, but non-interconnected portions of the filter wall and filter bottom. The particle trap operates to trap particles within the gap to prevent particles from passing beyond the filter bottom and into the microelectromechanical system.
Various refinements exist of the features noted in relation to the subject particle filter. Further features may also be incorporated into the particle filter to form multiple examples of the present invention. These refinements and additional features will be apparent from the following description and may exist individually or in any combination. For instance, the particle filter may also include a filter top. In this regard, the filter wall may be formed as part of the filter top, which in turn is a portion of a cover for the microelectromechanical system. Further, in this regard, the particle filter may be formed so that the filter wall encloses an area circumscribing one or more etch release apertures formed in the cover to prevent particulate contamination through the same.
The filter bottom on the other hand, may be formed in a plurality of geometric configurations to accommodate spatial limitations within a microelectromechanical system. In this regard, the filter wall may overlap a top portion of the filter bottom to define a particle trap that includes a substantially right angle at the overlap of the filter wall and filter bottom to improve efficiency.
In carrying out the above objects, and other objects, features, and advantages of the present invention, a microelectromechanical system is provided that includes at least a substrate material having at least one micro-device formed on the substrate material. The microelectromechanical system also includes at least one particle filter to prevent particles from entering the microelectromechanical system. Various refinements exist of the features noted in relation to the subject microelectromechanical system. Further features may also be incorporated into the microelectromechanical system to form multiple examples of the present invention. These refinements and additional features will be apparent from the following description and may exist individually or in any combination. For instance, the microelectromechanical system may also include a cover having at least one etch release aperture. In this regard, the particle filter may be formed between the cover and the substrate material around the at least one etch release aperture to prevent particulate contamination through the etch release aperture.
In carrying out the above objects, and other objects, features, and advantages of the present invention, a method of fabricating a particle filter for a microelectromechanical system is provided. The method includes the step of depositing and patteming a plurality of alternating layers of filter forming material and sacrificial material on a substrate material to form at least one filter bottom and at least one filter wall. The method also includes removing the sacrificial material to release the at least one filter bottom and the at least one filter wall to define a particle trap between mating but non-interconnected portions of the filter bottom and the filter wall.
Various refinements exist of the features noted in relation to the present method. Further features may also be incorporated into the present method to form multiple examples of the invention. These refinements and additional features will be apparent from the following description and may exist individually or in any combination. For instance, the filter bottom and filter wall may be interconnected by at least one support feature. In another instance, the method may further include forming the filter wall as part of the filter top, which in turn is a portion of a cover for the microelectromechanical system. Further, in this regard, the particle filter may be formed so that the filter wall encloses an area circumscribing one or more etch release apertures formed in the cover to prevent particulate contamination through the same. The method may further include patterning the filter bottom into a predetermined one of a plurality of geometric configurations to accommodate spatial limitations in a microelectromechanical system. In this regard, the filter wall may overlap a top portion of the filter bottom to define a particle trap that includes a substantially right angle at the overlap of the filter wall and filter bottom to improve efficiency.
In the context of the present invention, the first, second, and third, etc. connotations used in reference to the layers are used for the purpose of differentiating between different layers and are not used to indicate a fabrication sequence or structural sequence.